As a conventional method comprising the steps of: irradiating the pulse laser light (pulsed laser irradiation) to a compact body composed of various powders; releasing particles as finely atomized component thereby to generate fine particles having a particle diameter of nanometer order, such a conventional method has been mainly performed in a gaseous phase under pressure-reduced condition such as in a vacuum vessel.
In comparison with the above conventional gaseous phase laser ablation method, there has been eagerly developed and advanced the liquid phase laser ablation method in which the ablation operation is performed in the liquid phase in view of the following advantageous points:
a) an amount of scatter of the nanoparticles is small, and all of the generated nanoparticles can be utilized as a product;
b) a highly-cost vacuum equipment is not necessary, a structure of the equipment or facility therefor can be simplified and a facility cost is low;
c) a particle size distribution of the generated nanoparticles is sharp, and a scattering (variation) in the particle size is small;
d) the generated nanoparticles do not contact ambient air, so that impurities are not mixed into the nanoparticles as the product, so that the nanoparticles having high purity can be obtained;
e) the generated nanoparticles cause less agglomeration in the liquid phase than in the gaseous phase, and the nanoparticles can be taken out in a state where the nanoparticles are uniformly dispersed in the liquid phase; and the like.
FIG. 8 shows an example of a structure of the conventional liquid phase laser ablation apparatus disclosed in Japanese Patent Application (Laid-Open) Publication No. 2004-90081 (Patent Document 1). A laser light L oscillated from the laser oscillation device 21 is reflected by a reflecting mirror 22 toward a direction of a liquid 24, and vertically enters in a liquid surface.
Namely, the above-mentioned liquid phase laser ablation apparatus disclosed in the above Patent Document discloses a method comprising steps of: immersing a target 32 in the liquid 24 stored in a vessel (cell), the target 32 containing a component to be atomized; irradiating a laser light L which is focused by a focusing lens (collecting lens) 23 onto a surface of the target 32 from upward direction, and generating nanoparticles of, for example, metal, oxide, organic compounds, or the like that constitute the target 32.
Moreover, FIG. 7 shows another example of a structure of the conventional liquid phase laser ablation apparatus disclosed in Japanese Patent Application (Laid-Open) Publication No. 2006-122845 (Patent Document 2).
Namely, the above-mentioned Patent Document 2 discloses a liquid phase laser ablation apparatus in which a penetration hole 16 is provided to a side wall of the vessel 11 composed of glass with which the liquid 24 is filled, and a laser light introduction window (window body) 14 is fitted in the penetration hole 16.
The target 32 is immersed in the liquid 24 stored in the vessel 11. The laser light L which is oscillated in a horizontal direction form the laser oscillating device 21 is focused (converged) by the focusing lens 23 so that a focus of the laser light L is formed on a surface of the target 32. Thereafter, the focused laser light L is irradiated in a horizontal direction to the target 32 through the laser light introduction window 14. As a result, the component of the target 32 is generated as finely atomized particles having a form of atom, molecule, ion, or cluster-shape.